The present invention relates to a network of a data center in which a plurality of virtual machines are coupled through a plurality of network apparatuses.
In recent years, use of data centers in applications such as cloud services has been developing in order for individuals, corporations, and organizations to utilize computer resources and applications in a flexible and inexpensive manner.
In such data centers, many host computers and resources such as storage and appliances (firewalls, load balancers, management apparatuses, and the like) are coupled through a network to more than one data center at times.
Also, it is in general practice to consolidate resources using server virtualization techniques and improve resource efficiency and resource mobility in order to provide such resources rapidly and at low cost.
In data centers, it is necessary to on the one hand couple resources of the same user while on the other hand separating resources of different users, and conventionally, a technique known as a virtual local area network (VLAN) in which identifiers are assigned to transmission packets to logically separate networks was used in order to couple and separate resources.
However, as a result of advances in resource consolidation due to server virtualization techniques, deficiencies of VLAN have become a problem.
Additionally, in a server virtualization environment, virtual machines are coupled to virtual switches installed as software on a host computer, and thus, maintaining transmission performance particularly between virtual machines and monitoring such transmissions has become a problem.
Various solutions have been considered in order to deal with deficiencies of VLAN and problems of data centers such as maintaining transmission performance between virtual machines and monitoring such transmissions.
Network virtualization techniques have been considered in order to deal with deficiencies of VLAN. For example, Patent Documents 1, 2, and 3 disclose network virtualization technique in which a virtual switch on a host computer is used in order to encapsulate transmissions between virtual machines.
Also, a technique of realizing higher transmission performance between virtual machines and collective monitoring of a network by performing switching processes for transmission between virtual machines using physical network apparatuses (hereinafter referred as “hardware offloading” or simply as “offloading”) has been considered in order to maintain transmission performance between virtual machines and monitoring of such transmissions, and offloading has been disclosed in Patent Document 4 and Non-Patent Document 1, for example.    Patent Document 1: US Patent Application Publication No. 2013/0058215    Patent Document 2: U.S. Pat. No. 7,515,589    Patent Document 3: U.S. Pat. No. 8,223,770    Patent Document 4: WO 2007/146274